A common form of electric light socket has a built in control switch to enable the lamp or light fixture to be turned on and off at the socket itself rather than by means of a remotely located switch. Traditionally, the control switch has been of the mechanical form which has a stem and rotatable knob that protrude from the side of the socket.
Rotary mechanical switches of this type wear rapidly and are notoriously prone to failure after repeated cyclings of the switch. Switch failure is particularly common in multi-level lighting fixtures which enable selection of any of a plurality of different levels of illumination as the switches for such fixtures are necessarily more complex.
Electronic switching circuits having solid state components are not subject to mechanical wear and thus can be much more durable in the absence of adverse environmental conditions. Such switching circuits are also more convenient to operate as the circuit can be controlled by simply touching an electrically conductive input component.
It has heretofore been recognized that touch operated electronic switching circuits can be substituted for the traditional mechanical switch in electric lamps or can be added on to existing lamps which have a mechanical switch by means of a supplementary socket which screws into the pre-existing socket of the lamp Such circuits operate in response to changes of capacitance at an input terminal that result from contact of an operator's finger with the terminal or with electrical conductors that are connected to the terminal. The touch controlled lamps or supplementary light sockets are usually constructed to establish an electrical connection between the switching circuit input terminal and metallic portions of the lamp base or other lighting fixture. Thus the lamp or other lighting fixture can be turned on and off by simply touching some metallic portion of the lamp or fixture.
The solid state circuit components which control the voltage that is applied to the bulb in touch operated switching circuits are susceptible to heat damage and can be unreliable or fail if subjected to overheating. Typically such components may have a maximum temperature tolerance of about 80.degree. C. Such components inherently generate heat when conducting current and this must be dissipated to avoid a damaging temperature build-up. The problem is particularly acute in the context of a light socket as the light bulb itself produces heat and the socket can become very hot. Conventional heat sink arrangements for solid state circuit components may be inadequate in this context particularly if if a very high wattage bulb is engaged in the socket.
One effect of this problem is that prior touch operated light sockets are not suitable for use with very high wattage light bulbs. Use of a 300 watt bulb, for example, will very probably cause circuit failure from overheating.
Prior touch operated lighting installations have also required that the lamp as a whole have a specialized construction to accommodate the touch control circuit or, alternately, the complication of adding a supplementary socket to the pre-existing mechanically operated socket has been necessary. Prior touch controlled lamps or lighting fixtures are also unsuitable for use at elevated locations that cannot be conveniently reached by an operator.
The present invention is directed to overcoming one or more of the problems discussed above.